In the chemical industry, it is desirable to recycle costly heavy metals used in various chemical processes, to reduce processing costs. Recycling heavy metals is also desirable because it reduces pollution of the environment.
Plastics which are plated with heavy metals are used in a variety of applications, including the semiconductor and construction industry. Plated plastics are also used for radio parts, automobiles and other vehicles, and decorative wares. These plastics can be stripped of their heavy metals, and the metals can be reclaimed for use in other applications.
The most common prior art process used to strip metals from plated plastics is a ferric chloride leaching process. The plated plastics used in this process typically are coated with three layers of heavy metals. The plastic material is coated with a copper inner layer, and the outer layers are comprised of nickel and chromium. FIG. 1 shows a diagrammatic illustration of the prior art method of stripping plated plastics by ferric chloride leaching.
In the prior art method, the plated plastics are first crushed into smaller particles. The heavy metals are then "leached" from the plastic or dissolved into solution by treatment with ferric chloride. Thus, all three layers of heavy metal, copper, chromium and nickel, are dissolved into solution with each other. This is represented by the redox Equations 1 and 2, shown below. ##EQU1##
The plastic is stripped free of the metals, but the metals are not separated distinctly from each other. Therefore, the metals are not in a form in which they can be reused and the cost of separating them from each other is extremely high.
After leaching with ferric chloride, the copper in solution is cemented to low grade powder as represented by Equation 3 below. EQU Cu.sup.2+ +Fe.sup.0 .fwdarw.Fe.sup.2+ +Cu.sup.0 [ 3]
The chromium and nickel metals, however, fail to be separated effectively from each other due to their similar chemical properties. These metals accumulate in large quantities with each successive treatment of plated plastic sample by the ferric chloride solution. This results in heavy accumulation of nickel and chromium in the spent liquor of the process, causing accumulation of toxic pollutants.
After the cementation step, the spent ferrous chloride liquor is chlorinated to regenerate a ferric chloride solution as shown by Equation 4 below. EQU 2Fe.sup.2++Cl.sub.2 .fwdarw..sup.2 Fe.sup.3+ +2Cl.sup.- [ 4]
The ferric chloride solution can then be reused to treat successive plated plastics and strip heavy metals from them.
The prior art ferric chloride method has several disadvantages. The valuable metals of nickel and chromium are unable to be separated distinctly and economically from each other. In addition, due to the heavy pollutants which result in ferric chloride processing, this method is very costly.
Accordingly it is an object of the present invention to provide a process for stripping plated plastics in which heavy metals are separated from each other and recovered in a form which can be reused in other chemical processes.
Another object of the present invention is to provide a process for stripping plated plastics which reduces pollution of the environment.
It is a further object of the present invention to provide a process for stripping plated plastics which is less costly than prior art methods.
It is a further object of the present invention to provide a process for stripping plated plastics in which heavy metals can be reclamated in high yield without chemical processing, thereby making the process more economical.
The process for stripping plated plastics of the present invention has other objects and features of advantage which will become apparent from, or are set forth in more detail in, the accompanying drawings and the following description of the Best Mode of Carrying Out the Invention.